Magnetic pickup with inducing magnet axially aligned with the armature



1 MASANOBU CHO 3,538,266

MAGNETIC PICKUP WITH INDUCING MAGNET AXIALLY ALIGNED WITH THE ARMATUREFiled July 16. 1968 2 Sheets-Sheet l INVENT OR ATTORNEYS MASANOBU CH0 3,

MAGNETIC PICKUP WITH'INDUCING MAGNET AXIALLY ALIGNED WITH THE ARMATUREFiled July 16, 1968 2 Sheets-Sheet 2 3,538,266 MAGNETIQ PICKUP WITHINDUCING MAGNET AXIALLY ALIGNED WITH THE ARMATURE Masanobu Cho, Tokyo,Japan, assignor to Micro Seikr Company, Limited, Tokyo, Japan Filed July16, 1968, Ser. No. 745,177 Claims priority, application Japan, Oct. 6,1967, 42/6 1,074 Int. Cl. H041: 11/12 US. Cl. 179100.41 9 ClaimsABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of theinvention This invention relates to a pickup cartridge, and moreparticularly to an electromagnetic phonograph pickup cartridge for usewith stereophonic record discs.

DESCRIPTION OF THE PRIOR ART A conventional stereophonic pickupcartridge of moving magnet type is arranged so that a cantilever armhaving at one end a stylus is provided at the other end with a magnet,the magnet being supported by a rubber damper within a space defined bytwo pairs of pole pieces. The conventional device of this kind utilizesthe principle that oscillation of the stylus produced by variation alongthe record groove is transmitted mc chanically to the magnet foroscillating it to produce changes in the magnet fluxes within the polepieces, so that an output signal voltage is generated in the coils. Thisconventional moving magnet type cartridge has the drawback that thecartridge inherently has a larger oscillating mass than the stylus andhas poor practical efficiency. An attempt has been made to eliminatethis drawback by replacing the damper with a damper of softer rubber soas to make the compliance greater. The use of the softer damper hasresulted in unstable central support of the magnet. A use of a magnet oflarger capacity will result in reproduction of wave distortion inoperation due to magnetic inertia as well as in generation of unbalancedoutput voltages in the right and the left channel coils.

There is an induced magnet type pickup cartridge having a magnet whichis disposed substantially in parallel and laterally aligned relationshipto an armature somewhat spaced from the pole faces of the pole piecesin- 31,538,266 Patented Nov. 3, 1970 serted into coils, the coils beingadapted to generate output signal voltages as the armature which ismagnetized by the magnet mechanically oscillates according to variationalong the record groove.

This conventional pickup has the disadvantage that as the magnet isprovided in parallel to the armature and the cantilever arm and beinglocated forwardly apart from the armature, it has a Worse magnetizingefiiciency than the magnet for the armature. As a consequence, arelatively large magnet and armature are required and the oscillationmass cannot be sufficiently reduced.

In general, the stylus is subjected to traction produced by the frictionbetween the stylus and the record groove and effective rearwardly ofrelative advancement of the stylus with respect to the record.Therefore, the cartridge has the shortcoming that the damper for holdingthe oscillation unit is rearwardly biassed and, thus, is deformedresulting in an indefinite oscillation fulcrum point or pivotal pointfor the unit, which in turn will convert a simple oscillation intocomplicated one, resulting in a distortion in sound reproduced by virtueof mechanical oscillation caused by variation along the record groove.

SUMMARY OF THE INVENTION The present invention aims to provide a noveland advantageous pickup cartridge in which the above drawbacks have beeneliminated.

A primary object of the present invention is to provide a phonographpickup cartridge which is capable of magnetizing an armature veryefficiently and is of a reduced oscillation mass in its stylus assemblyand utilizes extremely small stylus pressure.

Another object of the present invention is to provide a phonographpickup cartridge in which the traction imparted to the stylus duringreproduction operation of a record disc is cancelled so thatreproduction of sounds is carried out without any distortion.

A further object of the invention is to provide a small stylus pressurepickup cartridge which is provided with means for readily indicating asto whether or not the stylus pressure is a predetermined value whenadjusting the stylus pressure so that the damper for holding thearmature is not deformed or distorted and is in its neutral position.

A still further object of the present invention is to provide a pickupcartridge of the kind that has a reduced number of turns in the coilsand a reduced magnetic inertia, and is able to take an increasedcompliance and to reproduce a better quality of sound. free from anydistortion and utilizes a readily replaceable stylus assembly.

Other objects and features of the presentinvention will be made apparentfrom the description which will be made hereunder with reference to theaccompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a major partof an embodiment of the pickup cartridge of the present invention withparts shown in longitudinal section;

FIG. 2 is a perspective view of the cartridge shown in FIG. 1;

FIG. 3 is a longitudinal side view of another embodi ment of thecartridge;

FIGS. 7, 8 and 9 are side views of the cartridge of the embodiment shownin FIGS. 4 and with a part being broken away in the respective figures,illustrating positions of the cartridge in stylus pressure adjusting operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment shown in FIGS. 1and 2 is a stereophonic pickup cartridge of induced magnet type. As willbe seen in these figures, there are four pole pieces 10, 11, 12, and 13disposed such that they are angularly spaced from one another by 90degrees, each of the pole pieces having its opposite ends turned atright angles from the major portion thereof. The pole pieces 1t] to,

13 are provided with coils 14, 15, 16 and 17 wound around the polepieces, respectively. The coils 14 and 16 around the pole pieces 10 and12, respectively, are connected together in series so that the inducedvoltages in the coils are added together, The coils and 17 around thefacing pole pieces 11 and 13 are also seriesconnected for the samereason. As an example, the coils 14 and 16 have lead wires 18 and 19extending outwardly therefrom, respectively, and both coils 14 and 16are connected by a lead wire 20, as shown in FIG. 1. A tubular holder 21of square configuration in section is secured to the turned end faces ofthe respective pole pieces 10 to 13. The holder 21 has a permanentmagnet 22 mounted thereon adjacent the rear end of the holder so thatthe magnetic poles are on an extension of the axis of the holder. Thereis provided a cantilever arm 23 having a stylus 24 mounted thereon atthe forward end thereof and an armature 25 of ferromagnetic materialsuch as pure iron or permalloy. Within the holder 21 is positioned arecess damper 26 of rubber in contact with the outer or forward end ofthe magnet 22. The rear or inner end of the armature 25 is received inthe recess of the damper 26, so that the rear end face of the armatureis spaced from the magnet 22 by the damper 26. The magnet 22 is providedrearwardly of the armature 25, appreciably spaced therefrom, and is onthe line of the axis thereof. This arrangement can magnetize thearmature 25 very efficiently. Thus the armature 25 can be small enoughand the oscillation mass of stylus may be tolerably small. Thereproduction characteristic in the high frequency range is especiallyexcellent.

When the stylus 24 traces a stereophonic record groove carryingstereophonic information on the opposing side walls of the groove, thearmature 25 which is being magnetically energized by the magnet 22 isoscillated in accordance with the modulation in the groove. Assumingthat the armature 2.5 is moved toward the pole piece 10, there isproduced an increase in the magnetic flux passing through the pole piece10 and a decrease in the magnetic flux passing through the pole piece 12which is positioned diametrically opposite to the pole piece 10. At thistime, the magnetic flux passing through the pole pieces 11 and 13 arereduced to some extent, but this reduction in magnetic flux is taken upby the coils 15 and 17 and, thus, no output voltage is generated.Therefore, an output signal voltage is obtained from the coils 14 and16. In the case Where the armature 25 is moved in the oppositedirection, the coil circuit operates in the reversed manner. Thus, thedevice is operable to faithfully reproduce the information recorded onthe stereophonic groove in whatever direction, i.e., in vertical orhorizontal or in what ever direction the oscillation may be.

When the stylus is in contact with a groove in a rotating record toreproduce information carried by the groove, the stylus is subjected totraction forces (arrow A) which are effective rearwardly of the relativeadvancement of the stylus with respect to the record due to the frictionbetween the stylus and the groove to thereby pull the cantilever arm 23and the armature 25 resulting in distortion thereof. With the cartridgeaccording to the present invention, however, the rear end of thearmature 25 is pulled 0r attracted by the magnet 22 in the directionopposite to that of said traction forces and, thus, the traction forceson the stylus, cantilever arm and the armature are mainly offset orcancelled by the attraction of the magnet 22. Therefore, the cantileverarm 23 and the armature 25 may be oscillated without being subjected toany distortion and may have their definite fulcrum or pivotal point forthe oscillation, affording highly faithful and superior reproduction.

FIG. 3 illustrates a cartridge of another embodiment of the presentinvention. The cartridge includes a housing 30 having fixed to the rearend thereof a terminal plate 32 on which are mounted four pins 31. Thecartridge also includes a cantilever arm 33 having a stylus 34 on theforward end and an armature 35 of ferromagnetic material on the otherend. The armature is supported by a damper 36 of rubber at substantiallythe intermediate portion of the armature. A permanent magnet 37 ismounted within the housing 30 so that the magnetic poles of the magnet37 is on an extension of the axis of the armature 35 and so that themagnet is somewhat spaced apart from the rear end face of the armature.There are provided two pairs of pole pieces 38, parallel to but spacedfrom the armature 35. Yokes 39 and 40 and coils 41 and 42 extendingtherearound, respectively, are provided in such a manner that the axesof the yokes and the coils are perpendicular to the axis of the armature35. On picking up modulation along the record groove, the stylus 34 andthe cantilever arm 33 are mechanically oscillated. This oscillation istransmitted to the armature 35. In response to the oscillation of thearmature 35, variations are produced in the magnetic fluxes passingthrough the yokes 39 and 40. Output signal voltages are generated in thecoils 41 and 42 and are led out of the coils.

The arrangement of the pickup cartridge of the instant embodimentprovides functional advantages similar to those obtainable from theconstruction of the preceding embodiment. In other words the magnet 37is provided rearwardly of armature 35 appreciably spaced from thearmature on the extended axis thereof so that it can very efiicientlymagnetize the armature 35 and, even if the armature 35 together with thestylus 34 and the cantilever arm 33 is subjected to traction forceseffective rearwardly of the relative advancement of the stylus withrespect to the record, such traction forces are effectively cancelled bythe attraction of the magnet 37 on the armature 35. The cantilever arm33 and the armature 35, therefore, are in no way distorted permitting inreproduction of high fidelity and excellence in sound quality.

The pickup of the instant embodiment has a further advantage that thematerial and the configuration of the magnet used may be selected freelyto some extent, as compared with a pickup of the conventional typewherein the magnet is adapted to be directly oscillated, so that it ispossible to generate an appropriate output voltage as well as to reducethe number of turns of the coils. Furthermore, the attraction force ofthe magnet 37 is effective to stabilize the intermediate support of thearmature 35, which makes it possible to form the damper 36 from a softrubber to thereby increase compliance greater. This also serves toprolong the effective lives of the record groove and the stylus.

FIGS. 4 to 6 illustrate still another embodiment of the cartridgeaccording to the present invention. The cartridge includes a housing 50moulded from a plastic material. The housing has secured on the rear endthereof a terminal plate 52 provided with four pins 51. Within thehousing 50 is contained an electromagnetic circuit means which isreceived in an outer shield 53 in the housing and comprises pole yokes56 and coils 57 bounded by and disposed above a coil block 54 and housedin an inner shield 55. A permanent magnet 58 is fixedly mounted at arearward position of a space defined between a lower portion of theouter shield 53 and the coil block 54. The outer shield 53 is providedwith an opening 59 for a stylus assembly which will be describedhereinafter. Four pole pieces 60 are fixed in a hole 61 into which thestylus assembly is inserted. Each of the coils 57 has lead wire 62respectively extending therefrom and secured by soldering to the pins 51at the inner ends thereof.

The stylus assembly consists of a stylus guard 63 so shaped anddimensioned as to be fitted into the hole 61, an armature 64 supportedby a damper 73 disposed within the guard 63, a stylus 66 provided on theforward end of a cantilever arm 65 whose rear end is secured to thearmature 64 and, a guard holder 67 for holding the guard 63 and aprojection 68 for use with a stylus pressure adjustment gauge. Thearmature 64 is supported at substantially its intermediate portion bythe damper 73 and is in tilted relationship with respect to the guard 63as shown in FIG. A when the stylus pressure against the record is zero(0). In this position of the armature 64, the damper 73 is deformed anddistorted. The projection 68 is adjustably provided in a bridge 70 whichis pivotally mounted on the holder 67 by means of an axle 69. The bridge70 is provided at the rotary end thereof with a pair of smallprojections 71A and 71B which are adapted to engage a stop 72 on theholder 67 for click-stopping the bridge 7 (l in essentially horizontalor vertical position.

The armature 64 is so positioned that the rear end face thereof isoffset inwardly from the rear end of the guard 63 by a distance d, sothat, when the stylus assembly is fitted and loaded into the cartridgehousing the guard 63 is inserted into the hole 61 until the rear end ofthe guard engages the magnet 58 and is stopped by the latter which willassure that the stylus assembly is mounted in the housing with thearmature rear end being spaced from the magnet 58 by the predetermineddistance d. The magnet 58 is essentially on the extended axis of thearmature when tracking so that it can very efliciently magnetize thearmature 64. The pickup can perform its function with the smallconstruction of the armature 64 allowing the armature to be minimized insize thereby keeping the oscillation mass of stylus small while thefrequency reproduction is much better. As the magnet 58 is fixed on thecartridge, the stylus assembly only, as shown in FIG. 6, can be replacedwhen the stylus is to be replaced which makes replacement veryeconomical. The armature 64 together with the stylus 66 and thecantilever arm 65 are subjected to traction forces eifective rearwardlyof the advancement of the stylus relative to the record, the cantileverarm 65 and the armature 64 are not distorted since the armature 64 isunder the attraction of the magnet 58. This is efiective to provide asound reproduction which is highly faithful to the original sound and isof excellent fidelity.

The use of the projection 68 for the stylus pressure adjusting gauge isseen in conjunction with FIGS. 7 to 9. While the initial position thatthe stylus assembly is mounted in the cartridge housing, the bridge 70is brought into horizontal position to make the projection 68 verticalas shown in FIG. 7. In this position, the stylus pressure against therecord 74 is zero (0) and the damper is, not being in its neutralposition, deformed. The stylus pressure is progressively increased untilthe forward end of the projection 68 reaches the surface of the record74 as shown in FIG. 8. The projection 68 is preliminarily adjusted inlength so that the stylus pressure is of optimum value when the pickupcartridge is in its position shown in FIG. 8. In this position, the axisof the armature 64 is parallel with the guard 63 and is coincident withthe axis of the magnetic pole of the magnet 58. The damper 73 is, thus,not deformed and is in its neutral position, assuring that the armature64 is precisely oscillated according to mechanical oscillation of thestylus 66. After completing the operation for increasing the styluspressure, the bridge 70 is turned upwardly about the axle 69 into arecess 75 in the housing 50. Reproduction operation of the record 74 isthen carried out in this state.

While the present invention has been described with reference to a fewparticular embodiments, it is to be understood that these embodimentsare only for illustrative purpose and the present invention may havevarious modifications and changes without departing from the spirit andthe scope of the invention as defined by the appended claims.

What is claimed is:

1. A phonograph pickup cartridge comprising an electromagnetic circuitincluding coils and pole pieces operatively disposed in a cartridgehousing; a replaceable stylus assembly including a cantilever arm, astylus at the forward end of said arm, an armature mounted on the rearend of said arm, a tubular guard member surrounding said armature, and adamper positioned. between said armature and guard member to movablymount said armature, arm and stylus therein; and a permanent magnetmounted in said housing substantially on the extended longitudinal axisof said armature when the stylus is in operable condition, said magnetbeing spaced from said rear end of the armature by a predeterminedamount so as to effectively magnetically energize said armature.

2. A phonograph pickup cartridge as claimed in claim 1 wherein said rearend of the armature is spaced a predetermined amount from the rear endof said guard member and when said replaceable stylus assembly is inposition in the housing said rear end of the guard member abuts thefront of said magnet thereby spacing said rear end of the armature bythe predetermined amount therefrom.

3. A phonograph pickup cartridge as claimed in claim 1 wherein saidcoils have axes substantially perpendicular to said armature axis, andlines extending the coil axes respectively pass through said polepieces.

4. A phonograph pickup cartridge as claimed in claim 1 wherein saiddamper also surrounds said rear end of the armature and is positionedbetween said rear end and said magnet, the dimension of damper rearwardthe armature determining the spacing.

5. A phonograph pickup cartridge as claimed in claim 1 wherein themagnetic axis of said permanent magnet is substantially on the extendedlongitudinal axis of said armature.

6. A phonograph pickup cartridge as claimed in claim 1 in which saidelectromagnetic circuit means comprises two pairs of pole piecesdisposed in opposite relation and having at their end turned portionsconnected to said said guard member; and a coil wound around each saidpole piece; said permanent magnet being fixed within the space enclosedand defined by said pole pieces, and said armature also being disposedWithin said space with a clearance between said armature and each of theend faces of said turned portions of the pole pieces.

7. A phonograph pickup cartridge as claimed in claim 1 in which the axesof said coils are substantially perpendicular to the axis of saidarmature; and said permanent magnet and said armature are external thespace between said coils.

8. A phonograph pickup cartridge as claimed in claim 1 wherein saidstylus assembly further includes a stylus pressure projection mounted onsaid guard member and rotatable to a first position essentiallyperpendicular to the record to be played and a second positionessentially parallel to the record, the projection being of anadjustable predetermined length, the lower end of which projection isadapted to contact the record when it is in said first position when adesired pressure is exerted on said stylus.

9. A phonograph pickup cartridge as claimed in claim 8 wherein saiddamper is deformed by said armature when there is no stylus pressure,and when the desired pressure is exerted on the stylus so that the lowerend of the projection contacts the record, said damper is in anundeformed state and said extended longitudinal axis of the armature isessentially coincident with the magnetic axis of said magnet.

References Cited STANLEY M. URYNOWICZ, JR., Primary Examiner 10 R. F.CARDILLO, 111., Assistant Examiner US. Cl. X.R.

